Demand for lithium-ion secondary batteries continues to grow with the dramatic increase in use of portable devices such as cellular telephones, tablet computers, and cameras that require high performance and reliability in their power sources. Along with this boost in the number of portable devices, the development of a power system for automobiles that does not rely solely on fossil fuels is becomingly increasingly important to producing an energy independent nation.
A generalized lithium battery includes an anode and a cathode that are disposed in a volume of a nonaqueous electrolyte material typically including one or more lithium salts and a solvent such as an organic carbonate material. In most instances, the anode and cathode have a body of separator material interposed therebetween. During the charging of the battery, lithium ions travel from the cathode to the anode and are intercalated therein. During discharge of the battery, the process reverses.
The high energy density of lithium ion secondary batteries makes these an attractive source of power for many markets. Small-size lithium ion secondary batteries historically use LiCoO2 as a cathode material along with a carbon based anode. Driving this is the superiority of LiCoO2 in terms of stable charge-discharge characteristics and high electronic conductivity. Unfortunately, these materials also suffer from high expense, biological toxicity, and reduced efficiency due to cobalt deposits.
Nickel containing mixed oxide materials offer a solution to the disadvantages of LiCoO2. These materials offer high capacities, often with a specific capacity of 200 mAh/g or greater. Among promising materials for cathodes, NiO2 or compositions where some of the nickel is replaced with cobalt, show excellent capacities, but suffer from sub-optimal cycle life as a result of their high oxidation power and oxygen release. For example, after only 5 and 10 cycles the capacity of NiO2 or Ni92Co8 drops from >200 mAh/g to <160 mAh/g.
Other materials have recently been combined with nickel hydroxides in an attempt to create a material with acceptable cycling characteristics. For example, U.S. Pat. No. 8,012,624 combines a mixed metal hydroxide with Ni(OH)2. While these materials were able to resist capacity losses in excess of 14% at 60 cycles, their specific capacity was dismal in comparison to Ni(OH)2 alone suggesting that this combination of materials may not provide the necessary characteristics for high energy demands.
While the desire for superior electrode materials for lithium ion batteries continues to grow, the materials necessary to satisfy the high demands of current and future market devices are still lacking. Thus, there is a need for new materials and methods for their production for use as a cathode in lithium-ion cells.
Disclosed are composite materials suitable for use as a cathode in a lithium ion cell. The materials of the present invention are relatively low in cost, and when incorporated into a battery system, manifest large charge storage capacities together with significantly improved cycle life. Methods of producing several embodiments of these materials allow formation of a specific molecular structure that is unexpectedly resistant to capacity losses during cycling. These and other advantages of the present invention will be apparent from the drawings, discussion, and description that follow.